Coal fired steam generating set is a steam power cycle system based on Rankine cycle and comprises a condensate-type generating set and a coal fired boiler generating set, the operational procedure of the coal fired steam generating set is as follows: raw coal is dried and crushed into coal powder via a coal grinding mill, the coal powder is fed into a boiler and combusted so as to release heat, water absorbs heat at a certain pressure in a steam drum of the boiler and evaporated into saturated steam. The saturated steam absorbs heat in a superheater and is changed into superheated steam, the superheated steam expands and does work to outside via a steam turbine, and a certain heat loss occurs. After the superheated steam has done work due to expansion in the steam turbine, exhaust steam at an outlet at a tail end of the steam turbine is fed into a condenser so as to perform cold-source heat dissipation and condense into water. The water is sequentially fed into a shaft gland heater and a multi-stage low pressure heater (i.e., a first low pressure heater, a second low pressure heater, a third low pressure heater and a fourth low pressure heater) and heated stage by stage; the heated water is fed into a deaerator for oxygen removal, enhanced in pressure via a water feed pump, fed into a multi-stage high pressure heater (i.e. a fifth high pressure heater, a sixth high pressure heater, a seventh high pressure heater, and a eighth high pressure heater) and reheated; the reheated water is fed into a coal economizer so as to be further heated in the boiler system, and then fed into the steam drum for steam-liquid separation; the saturated steam is discharged from the steam drum and fed into the superheater of the boiler, heated by the superheater of the boiler into superheated steam with a certain temperature, the superheated steam is fed into the steam turbine for generating electricity.
The above procedure has the following disadvantages.
A. The coal powder which is fed into a coal pulverizing system (such as a coal grinding mill, a coal grinding air blower, and so on) and a boiler contains moisture, the moisture will be evaporated in the coal pulverizing system and a furnace of the boiler, the required heat for evaporation of the moisture is supplied by a combustion heat result from the combustion of the coal powder self in the boiler, therefore it is necessary to consume a large quantity of the coal powder so as to evaporate the moisture contained in the coal powder.
B. During generating electricity by the superheated steam in the steam turbine, conversion rate from heat energy of the superheated steam to the electric energy is less than 50%, the reason for low generating efficiency lies in: with a process of heating a condensing water by extraction steam from the steam turbine, about one third of evaporation latent heat of the superheated steam is used, about two third of evaporation latent heat of the superheated steam can not be used and only is carried away by a condensing medium via the condenser so as to be dissipated via a water cooling tower or an air cooling island, so the latter part is a maximum heat consumption which can not be used, namely cold-source loss of the condensing-type generating set.